A conventional method of blocking access to specific video programs that are prejudicial to children, such as violent and obscene video programs, utilizes a designation of specific video program channels that are barred by video receivers, such as television receivers, video tape recorders, video disc players etc., to disable the video receivers upon receiving the specific video programs. This method relies on a so-called V-chip (Violence chip) which is embedded within video receivers as mandated by the Telecommunications Act of 1996 in USA. The system operates by using a transmitter and receiver. A transmitter side transmits rating information classifying violent or obscene degrees of video program contents by superposing the rating information on video signals and a receiver side changes scenes if the rating rank of the transmitted video program exceeds the other rating rank designated by an authorized person.
Among these methods, for preventing an illegal change of rating rank designated by an unauthorized person, there is such a method in which authorized person registers a password in designating the rating rank, and thereafter the video receiver automatically rejects illegal attempts to change the designation of the rating rank without correctly entering the registered password.
However, those systems still include problems as described below.
If an unauthorized person such as a child has found the registered password, the unauthorized person may to access restricted TV programs through illegally changing the designated rating rank. Furthermore, if the original designation made by the authorized person is restored after the illegal designation change, the authorized person would be unaware that the registered password was broken and the original designation of the rating rank had been changed without authorization.
An unauthorized person who has discovered the registered password is able to freely change the designation of the rating rank or restore it until the password is updated. However, as an authorized person is not aware that that the password has been accessed and is not motivated to update it, if the password has been once found by unauthorized person, the designation of rating rank could be illegally changed while the authorized person is not aware of it.
To avoid this, a periodical updating of the password by the authorized person, increasing of password characters, a combination of various security systems such as secret commands with a password would be advantageous. These approaches, however, make it difficult and complicated to designate the rating rank by the authorized person. In addition, until the authorized person becomes aware of the illegal change of the designation, there is no motivation to resequence the password.
As described above, according to a conventional method, if the designation of a video program rating was changed by any unauthorized person, the authorized person is not able to recognize that the designation of rating was changed by any unauthorized person. That is, an authorized person is unable to recognize whether his intention for blocking access to violent or obscene video programs is being achieved or not.